Clarify invocation order of componentDidMount

OP is delivering on promise made here: https://discuss.reactjs.org/t/how-do-you-invoke-the-render-callback-in-jsx/1744

docs/ref-03-component-specs.md

@@ -121,7 +121,7 @@ Invoked once, both on the client and server, immediately before the initial rend
 componentDidMount()
 ```
 
-Invoked once, only on the client (not on the server), immediately after the initial rendering occurs. At this point in the lifecycle, the component has a DOM representation which you can access via `React.findDOMNode(this)`.
+Invoked once, only on the client (not on the server), immediately after the initial rendering occurs. At this point in the lifecycle, the component has a DOM representation which you can access via `React.findDOMNode(this)`. The `componentDidMount()` method of child components is invoked before that of parent components.
 
 If you want to integrate with other JavaScript frameworks, set timers using `setTimeout` or `setInterval`, or send AJAX requests, perform those operations in this method.